Completely agree that this is perfectly normal behavior. The indicated voltage is a function of the battery's state of charge and loading at the time, and what the car's electronics are doing to charge the battery. As others have posted, it can go up to 15V or even a bit more.

Is it normal for alternator voltage to fluctuate?

When the battery's state of charge is low, the voltage is raised slightly to quickly put the charge back in. When the state of charge is high, the voltage is lowered slightly to prevent overcharging. If the vehicle has a voltmeter gauge, you may see the voltage move up or down. This is normal.

Should alternator voltage be steady?

The voltage should read a minimum of 13 volts. A good alternator should put out between **13.5-14.5 volts. Stress test the alternator - Place a load on the alternator by turning on the headlights, the radio and the air conditioning. The voltage should remain high with these circuits on.